Machines are already known for rolling very thick metal sheets or plates, particularly in shipbuilding, which machines generally incorporating four cylindrical rollers.
Two of the rollers, called the central rollers, are lying in a vertical plane and nip between themselves the sheet to be rolled, with a controllable effort. One of the rollers is mobile with respect to the other in a vertical plane by means of two cylinders that move it in such manner that the generating lines of the upper and lower central rollers are parallel. The feeding hydraulic pressure of the cylinders can vary and provides for the control of the nipping effort.
Moreover the nipping engagement provides for driving the metal sheet by friction lengthwise and in the horizontal plane, the two lower and upper central rollers being provided with rotation means such as an electric, hydraulic or other motor element.
Two other rollers, usually called side rollers, are placed symmetrically on both sides of the central rollers. They are mobile in a direction which is oblique with respect to the plane in which lie the axes of the two central rollers.
Two groups of hydraulic cylinders are attached to the side rollers, and are used for positioning separately in space the side rollers in altitude with respect to the pair of central rollers.
Of course, the aforementioned assembly of four rollers is incorporated in a support frame having all the slides necessary for the movements of the central and side rollers.
Moreover, the support frame is provided with a lateral rocking or tilting bearing articulated about an operation axis by a cylinder. This tilting bearing assembly is situated in the axis of a frame and is adapted for disengaging the upper central roller sliding bearing so as to be able to give, in the aforementioned assembly of four rollers, an entirely closed rolled metal sheet.
In present practice, the setting of the machine, and particularly setting of the position of the side roller forming the metal sheet theoretical radius, are controlled manually by an operator whose work, despite his experience, is satisfactory only after a long period of work. Consequently, the cost price is very high. This is also due to the fact that due to the non-homogeneities of the metal to be rolled, the metal sheet thickness variations due to laminating errors, the modifications of the metal characteristics during rolling, and the fact that the operation is carried out beyond the material resilient limit, it results on the one hand that the radius really obtained is not the one which is controlled and on the other hand that there is often found a really important evolution which evolution can be considered as variations between a maximum radius and a minimum radius really bound to each other. It is therefore necessary to make up for such errors by resorting to many lateral passes carried out at a reduced speed of the machine, with nevertheless a final result presenting non negligible faults.
This state of the prior art shows an insufficient quality of the work produced by the machine, despite an intervention of highly qualified experts.
Therefore, it has appeared necessary to remedy these major disadvantages in view of the very strict specification sheets recently in force in shipbuilding.